Practical Engineering: When a Block Foundation Cracks

For modestly priced homes in Georgia,
where I work, basement walls are usually
built with 8-inch concrete masonry
units (CMUs) — otherwise known as
concrete blocks. It's a relatively inexpensive
way to build a sound wall that
can be easily waterproofed.
Unfortunately, these walls are too often
built without any reinforcing steel, and
that's when the trouble begins.
What the Code Says
The 1992 CABO (Council of
American Building Officials) One &
Two Family Dwelling Code, in Table
R-304.3a, does allow the use of unreinforced
block walls. For 8-inch CMU
walls where the cores are not filled, the
maximum acceptable depth of unbalanced
fill is only 4 feet. ("Unbalanced"
means there is no earth on the inside of
the wall,